用Kubo形式计算双味夸克物质的输运系数
Transport coefficients of two-flavor quark matter from the Kubo formalism
摘要：
在双味Nambu-Jona-Lasinio模型下计算了夸克物质在非零化学势和温度下的输运系数。我们应用Kubo形式主义获得的热（$κ$）和电（$σ$）的电导率，以及更新的剪切粘度（$η$）通过评估相应的平衡两点相关函数，以领先的顺序在$1/N_c$扩展。自能和谱函数的狄拉克结构被考虑在内，因为这些是从质量壳夸克的介子交换Fock图中评估的。我们发现，热导率和电导率是温度和密度的递减函数以上的莫特温度$T_{\rm M}$的介子溶解成夸克，主要的贡献产生的时间和矢量分量的谱函数。对于不同密度，系数显示出对比率$T/T_{\rm M}$的普遍依赖性，即，结果的不同之处在于依赖于化学势的常数。我们还表明，比$σ/κ$的Wiedemann-Franz定律不成立。比率$η/s $（其中$s$是熵密度）具有接近莫特温度的单位数量级（或更大），并且随着温度升高，接近AdS/CFT结合$1/4π$。还证明了比率$κT/c_V $，其中$c_V$是比热，从下到上由$1/18$限定。
英文摘要：
The transport coefficients of quark matter at non-zero chemical potential and temperature are computed within the two-flavor Nambu--Jona-Lasinio model. We apply the Kubo formalism to obtain the thermal ($κ$) and electrical ($σ$) conductivities as well as an update of the shear viscosity ($η$) by evaluating the corresponding equilibrium two-point correlation functions to leading order in the $1/N_c$ expansion. The Dirac structure of the self-energies and spectral functions is taken into account as these are evaluated from the meson-exchange Fock diagrams for on-mass-shell quarks. We find that the thermal and electrical conductivities are decreasing functions of temperature and density above the Mott temperature $T_{\rm M}$ of dissolution of mesons into quarks, the main contributions being generated by the temporal and vector components of the spectral functions. The coefficients show a universal dependence on the ratio $T/T_{\rm M}$ for different densities, i.e., the results differ by a chemical-potential dependent constant. We also show that the Wiedemann-Franz law for the ratio $σ/κ$ does not hold. The ratio $η/s $, where $s$ is the entropy density, is of order of unity (or larger) close to the Mott temperature and, as the temperature increases, approaches the AdS/CFT bound $1/4π$. It is also conjectured that the ratio $κT/c_V $, with $c_V$ being the specific heat, is bounded from below by $1/18$.
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